The SNP’s flagship policy of a single national police force has been severely undermined by a report revealing that the £1.1 billion of savings promised by ministers might not materialise.

The investigation by the public spending watchdog has also laid bare the infighting between officials, police and government that was rife while Police Scotland was established. Audit Scotland’s report contains a litany of concerns about the process, including a revelation that the headquarters for the Scottish Police Authority (SPA) costs taxpayers £132,000 in rent a year — but has never been used.